[Alsa][gpSP] Sound is loud and saturated in some games with "asound.conf" configuration file

[DrUm78]

Sound is muddy and saturated with gpSP after Alsa downmixed sound fix in firmware 2.2.0. It's especially noticeable when sound is loud (70-100% volume) and through games with loud volume (Top Gear Rally is the best example I've found so far).
The issue here is that it would need to set gpSP to mono but this one does not like mono and sound is even worse in that case.

Steps to reproduce the behavior:

1. Launch Top Gear Rally (it's very noticeable with this one) at 100% volume
2. Reach the title screen
3. Notice that the music is muddy and very saturated
4. Exit gpSP
5. Rename or remove /etc/asound.conf
6. Launch Top Gear Rally again
7. Notice that the sound is not saturated, lower and clearer now

Expected behavior
Sound should stay clear and not saturated with Alsa fix as it is without it. Maybe the Alsa fix seems to set the gain too high here (2 sound channels mixed into one).

[DrUm78]

I fixed it the dirty way for gpSP: DrUm78/gpsp@d06aa87. At least that works. :)